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Renewable Energy Intermittency: Realistic Solutions for Asia

Most countries across Southeast Asia have embarked upon developing large scale wind and solar power plants. Thailand has pioneered the movement and has so far installed about 3.5 GW of generation capacity from these sources. Past the initial enthusiasm sparked by the dramatic decrease in cost of renewable technologies, concerns are now rising from the power network operators that the unpredictable intermittency of solar and wind resources could destabilize the grids and increase stress on the existing power plants.

What are the practical solutions to mitigate intermittency?

Grid power experts around the world advocate a global “smart grid,” where electricity demand of industry, transports, new energy storage plants and residential buildings would be automatically dispatched according to the energy instantaneously available. Cross-border transmission lines would also allow for rebalancing production and consumption at the level of the continent, as it is done in Europe for instance. Although the concept is indeed promising, there is a long way to go in a region where power systems haven’t been designed for it and national grids are hardly connected.

Fortunately, there are also easier means of re-balancing power networks in a preliminary stage. Pöyry, as a global consultant in the energy sector, is involved in multiple renewable energy projects across Asia and has a good vision on current and emerging technical solutions to mitigate intermittency. We interact with the main stakeholders (developers, lenders, authorities, suppliers, contractors) and advise on the following trending schemes.

Hybrid Power Plants and DispatchThe simplest and least expensive strategy to partially mitigate generation fluctuations by renewable power plants is to associate assets of different natures in a smart way, based on their statistical production patterns. One of the major costs of a large scale “smart grid” is the electrical transmission network. By grouping strategic assets, the grid requirements are much lower and the total cost of development strongly reduced.

A particularly interesting scheme of such synergy is the rising trend of floating solar PV plants on hydropower reservoirs. Pöyry has the chance to be involved in four large scale projects using this emerging technology. Instead of occupying precious land, solar panels are mounted on plastic floats assembled into a large pontoon that can withstand water level fluctuations of up to 40 meters. The system can be connected onto the same electrical lines as the hydro turbines, with limited additional cost.

Hydropower stations are known to be excellent at regulating production: when there’s a peak of power demand, turbines are activated and when energy is less needed, the gates are closed for later use of water. This can compensate for the drop of solar output due to a cloud or the night time. Moreover, there is an interesting seasonal complementarity between the high solar production during dry season, when hydropower is at its lowest, and vice-versa.

Given the large number of hydropower reservoirs across Asia, the region has a hybridization potential of multiple gigawatts, although contractual arrangements of existing systems may constitute a barrier to development in some cases.

Since 2017, the Ministry of Energy of Thailand has also opened bidding for hybrid power purchase agreements essentially oriented towards biomass and solar PV or wind to incentivize the deployment of regulated renewables. Even if other combinations are also welcome, the scheme is initially thought to use a biomass or biogas plant as regulating base to guarantee a firm generation during peak hours, eventually in association with other renewable sources. Some developers have proposed using battery storage to regulate the plant.

Energy StorageThis brings us to one of the hot topics of the moment: energy storage. In spite of the profusion of new experimental methods, only two main technologies offer a credible business model at the time being: pumped hydropower and batteries.

Pumped hydropower storage plants or “PSP” used to be the only relevant large scale model for over a century and still represents more than 95% of the total worldwide installed grid storage capacity. Excess electricity is used to pump water—for example from a river—to an artificial lake at a higher altitude. In mountainous countries like Laos, Vietnam and many others in Asia, the natural relief is very well suited and offers a rich potential for PSP. Pöyry has been involved in 35 PSP projects worldwide in the last 10 years only, including a number of schemes in Asia, and expects to see more opportunities arising in the region, to enable intermittent solar and wind plants developments.

Batteries have come to the headlines recently thanks to the fast drop in price. However, they apply to a different market segment than PSP. Their cost still remains too high to compete for storage longer than a few hours, but their unique feature is a tremendously fast reaction time. While hydropower generation can start to full capacity in a matter of minutes, Lithium batteries latency comes down to seconds or milliseconds! This agility, along with fast construction process and low requirements regarding the location, make it an increasingly attractive solution to complement solar plants by shifting the generation peak by a couple of hours, while stabilizing the entire power grid against second-scale fluctuations. We could then see “solar + battery” plants competing with gas peaking plants in the coming years for these applications, as indicates a recent research by Pöyry.

Demand-Side Response (DSR)Following the adage “the cheapest electricity is the electricity we don’t have to produce”, the same is true with energy storage: an important part of the mismatch between production and consumption can be avoided by simply deferring by a few hours the use of some appliances such as water heating, electrical vehicles charging, and some specific industries (large compressors, treatment plants,…) that are not strict on the timing of their operation. As reward for such flexibility, the users can benefit from more advantageous tariffs.A pilot project of the scheme has been initiated in Vietnam with Ho Chi Minh City Power Company and results will be awaited to define the next implementation stages. Although differential tariffs are already in use in most countries, with fixed peak and off-peak prices for energy, a more advanced DSR system would ideally enable a dynamic reaction of the demand to a given event (for instance a cloudy afternoon or a power plant failure).

ConclusionThe three classes of intermittency mitigation measures discussed in this article – hybridization, energy storage and local DSR – present practical, readily available solutions by order of cost and complexity of implementation. The typical roadmap featured in Figure 2 is a simplified vision of the successive stages leading to a power grid with a high integration of renewable energy sources. The current “opportunistic” development of renewable projects, based only on solar or wind resource availability, is currently possible thanks to the relatively low share they have in the energy mix. However, with the rise in renewable installed capacity, grids will be increasingly in need of regulation. Authorities are already starting to implement hybrid development plans, energy storage is in the air too and it is a safe bet that demand-side response will be part of future developments.

50MW

Some hybrid solar-hydro plants currently in development in Asia have capacity in the order of 50 MW.